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Questions and Answers
What is a key difference between smooth muscle and skeletal muscle contractions?
What is a key difference between smooth muscle and skeletal muscle contractions?
- Skeletal muscles respond to a variety of stimuli, while smooth muscles only respond to excitatory stimuli
- Smooth muscles contract faster than skeletal muscles
- Skeletal muscles create more tension over a long period of time (correct)
- Smooth muscles lack striations, while skeletal muscles have z lines
Where is actin bound in smooth muscles and what does it anchor to?
Where is actin bound in smooth muscles and what does it anchor to?
- Actin is bound to dense bodies and anchors to extracellular fluid (correct)
- Actin is bound to z lines and anchors to the sarcoplasmic reticulum
- Actin is bound to troponin and anchors to the ECF
- Actin is bound to myosin and anchors to the cytoplasm
How are neurons connected to smooth muscles compared to skeletal muscles?
How are neurons connected to smooth muscles compared to skeletal muscles?
- Neurons in smooth muscles form neuromuscular junctions with muscle fibers
- Neurons in smooth muscles are directly connected to each muscle fiber
- Neurons in smooth muscles are not directly connected like in skeletal muscles (correct)
- Neurons in skeletal muscles do not influence muscle contractions
Why do autonomic nerves connect to smooth muscles instead of somatic nerves?
Why do autonomic nerves connect to smooth muscles instead of somatic nerves?
What is a distinguishing feature of autonomic neurons at the junction of smooth muscles?
What is a distinguishing feature of autonomic neurons at the junction of smooth muscles?
What is the neurotransmitter released by autonomic nerves?
What is the neurotransmitter released by autonomic nerves?
Which system is associated with norepinephrine?
Which system is associated with norepinephrine?
What type of muscle undergoes mitosis and hyperplasia?
What type of muscle undergoes mitosis and hyperplasia?
What is the purpose of the circular arrangement of smooth muscle in the viscera?
What is the purpose of the circular arrangement of smooth muscle in the viscera?
Which type of smooth muscle can contract as a unit due to gap junctions?
Which type of smooth muscle can contract as a unit due to gap junctions?
How can calcium concentration decrease in a smooth muscle cell?
How can calcium concentration decrease in a smooth muscle cell?
Which of the following is a direct effect of parasympathetic innervation?
Which of the following is a direct effect of parasympathetic innervation?
Where is the primary concentration of sympathetic innervation?
Where is the primary concentration of sympathetic innervation?
Which type of cholinergic receptor is classified as second messengers?
Which type of cholinergic receptor is classified as second messengers?
What is the primary action of alpha 2 adrenergic receptors?
What is the primary action of alpha 2 adrenergic receptors?
What is the primary neurotransmitter that alpha 1 adrenergic receptors respond to?
What is the primary neurotransmitter that alpha 1 adrenergic receptors respond to?
Which drugs are commonly used to block beta 1 adrenergic receptors?
Which drugs are commonly used to block beta 1 adrenergic receptors?
What is the triad of symptoms associated with Horner’s syndrome?
What is the triad of symptoms associated with Horner’s syndrome?
How is acetylcholine removed from a synaptic cleft?
How is acetylcholine removed from a synaptic cleft?
What is the primary role of beta 1 adrenergic receptors?
What is the primary role of beta 1 adrenergic receptors?
What is the role of Ca-Calmoudilin in smooth muscle contraction?
What is the role of Ca-Calmoudilin in smooth muscle contraction?
In smooth muscle contraction, what is the significance of myosin ATPase?
In smooth muscle contraction, what is the significance of myosin ATPase?
What factor contributes to maintaining a long period of tension in smooth muscle contraction?
What factor contributes to maintaining a long period of tension in smooth muscle contraction?
Which neurotransmitter is released from the adrenal glands during adrenal innervation?
Which neurotransmitter is released from the adrenal glands during adrenal innervation?
What is the main function of postganglionic fibers in the
autonomic nervous system?
What is the main function of postganglionic fibers in the autonomic nervous system?
In sympathetic innervation, where does acetylcholine (ACH) get released instead of Epinephrine (EP) and Norepinephrine (NE)?
In sympathetic innervation, where does acetylcholine (ACH) get released instead of Epinephrine (EP) and Norepinephrine (NE)?
What is the main neurotransmitter released from the presynaptic neuron in a typical neuron?
What is the main neurotransmitter released from the presynaptic neuron in a typical neuron?
What is the function of phosphatase in smooth muscle contraction?
What is the function of phosphatase in smooth muscle contraction?
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Study Notes
Smooth Muscle vs. Skeletal Muscle
- Lack striations, less myosin, no troponin (calmodulin)
- Dense bodies instead of Z lines
- Involuntary, responds to stretch, chemicals, temperature
- Ca2+ from ECF, less developed SR
- Slow, sustained contractions
Characteristics of Smooth Muscle
- Actin bound to dense bodies, anchored to ECF and other smooth muscles
- Creates work through contraction
- Located in vessels (tunica media)
- Not directly connected to neurons, no neuromuscular junction
- Innervated by autonomic nerves (not somatic)
- Autonomic neurons contain varicosities (swellings with NT storage)
- Release norepinephrine and acetylcholine
Types of Smooth Muscle
- Multi-unit smooth muscle:
- Can have own autonomic nerve connection
- Does not fire spontaneously
- Does not contract in response to stretch
- Single-unit smooth muscle:
- Contains gap junctions
- Contracts as a unit (AP propagates from cell to cell)
- Can be spontaneously active (fluctuating threshold potential)
- Stretch can induce contraction
Stimulating Smooth Muscle
- Autonomic nerves (excite or inhibit)
- Chemicals (hormones, CO2, O2, NO, low pH, temperature, stretch)
- Ca2+ concentration increase:
- "Leak channel"
- Voltage-gated channel
- Ligand-gated channel
- Stretch-activated channel
- IP3 pathway
- Calcium-induced calcium release
- Ca2+ concentration decrease:
- Ca ATPase out of the cell
- Ca ATPase into the SR
- Ca2+/Na+ countertransporter
Smooth Muscle Contraction Pathway
- Ca2+ enters via Ca2+ channels
- Ca2+ binds to calmodulin to form Ca-calmodulin
- Ca-calmodulin activates myosin light chain kinase (Ca-calmodulin MLCK) complex
- Phosphorylates light chain on myosin head (1) and activates myosin ATPase
- Myosin heads bind to actin and pull actin back toward its tail
- Actin pulls on dense bodies and the cell contracts
- ATP comes back and removes the myosin head from actin and resets the cross-bridge cycle
Phasic Contraction and Tonic Contraction
- Phasic contraction: similar to skeletal muscle contraction
- Tonic contraction (latch bridge mechanism):
- Myosin head binds to actin and waits for ATP to come in and remove myosin head
- Phosphatase comes in and cleaves Pi, leaving myosin head bound to actin without Pi
- ATP has lessened affinity to bind and remove myosin head, maintaining tension
Autonomic Nervous System (ANS)
- Visceral efferent motor
- Innervates smooth muscle, cardiac muscle, and glands
- Sympathetic and parasympathetic divisions
- Sympathetic: "fight or flight" response
- Parasympathetic: "rest and digest" response
- Both divisions work in tandem, never fully turning off or on
Sympathetic and Parasympathetic Innervation
- Sympathetic:
- Preganglionic neurons: T1-T12 and upper 2-3 segments of the spinal cord
- Postganglionic neurons: short, unmyelinated
- Receptors: alpha and beta adrenergic
- Parasympathetic:
- Preganglionic neurons: cranial nerves 3, 7, 9, and 10, and sacral portion of the spinal cord
- Postganglionic neurons: long, unmyelinated
- Receptors: muscarinic and nicotinic cholinergic
Adrenergic and Cholinergic Receptors
- Adrenergic receptors respond to norepinephrine (NE) or epinephrine (EPI)
- Alpha and beta receptors:
- Alpha 1: smooth muscle, visceral organs (GI tract), vasoconstriction
- Alpha 2: presynaptic, inhibits NE release
- Beta 1: heart, increases rate and contractility
- Beta 2: respiratory, uterine, and GI smooth muscle, vasodilation
- Cholinergic receptors respond to acetylcholine (ACH)
- Muscarinic and nicotinic receptors:
- Muscarinic: second messenger
- Nicotinic: ligand-gated
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